Structure of amorphous materials in the NASICON system Na_1+xTi₂Si_xP₃−xO₁₂

The structure of glasses in the sodium (Na) super-ionic conductor (NASICON) system Na_1+xTi₂Si_xP₃−xO₁₂ with x = 0.8 and x = 1.0 was explored by combining neutron and high-energy x-ray diffraction with ²⁹Si, ³¹P and ²³Na solid-state nuclear magnetic resonance (NMR) spectroscopy. The 29Si magic angle spinning (MAS) NMR spectra reveal that the silica component remains fully polymerized in the form of Si⁴ units, i.e. the silicon atoms are bound to four bridging oxygen atoms. The ³¹P{²³Na} rotational echo adiabatic passage double resonance (REAPDOR) NMR data suggest that the ³¹P MAS NMR line shape originates from four-coordinated Pn units, where n = 1, 2 or 3 is the number of bridging oxygen atoms per phosphorus atom. These sites differ in their ³¹P-²³Na dipolar coupling strengths. The results support an intermediate range order scenario of a phosphosilicate mixed network-former glass in which the phosphate groups selectively attract the Na⁺ modifier ions. Titanium takes a sub-octahedral coordination environment with a mean Ti–O coordination number of 5.17(4) for x = 0.8 and 4.86(4) for x = 1.0. A mismatch between the P–O and Si–O bond lengths of 8% is likely to inhibit the incorporation of silicon into the phosphorus sites of the NASICON crystal structure.

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Recommended citation: Rita Mendes Da Silva, Anita Zeidler, Henrik Bradtmüller, Hellmut Eckert, Henry E Fischer, Chris J Benmore and Philip S Salmon, “Structure of amorphous materials in the NASICON system Na_1+xTi₂Si_xP₃−xO₁₂”, Journal of Physics: Condensed Matter, 2023, 35, 274002.